The present state of forced air cooling to rapidly remove field heat from recently harvested produce is well known. Typical techniques utilizing force air cooling are disclosed in the publication “Commercial Cooling of Fruits and Vegetables” by Thompson et al, available through the University of California, Agriculture and Natural Resources Communication Services, Oakland, Calf. 94608, U.S. Pat. No. 4,123,917 issued to Curtis et al., and U.S. Pat. No. 4,532,774 issued to Burns.
Generally, harvested produce is packed into containers or bins. The cooling procedure to remove field heat from the produce is performed by utilizing high capacity fans that pull refrigerated air through the produce. Forcing refrigerated air to come into contact with warm produce at high speeds results in the rapid convective cooling of the produce. The cooling of the produce in a uniform manner is objective. Uneven cooling of the produce can result in damaged produce or produce not cooled to a sufficient temperature.
A process for forced air cooling is known as tunnel cooling within a cooling room. The process includes creating an air tunnel by placing two parallel rows of palletized boxes with a space between the rows. The top and ends of the pallets are covered with a tarp. The space between the rows of pallets, above the floor, and under the covering tarp forms a tunnel, otherwise known as a return air plenum.
The typical prior art design for implementing this process includes a refrigeration unit provides high pressure, refrigerated air into the cooling room. The walls, floor, and ceiling of the cooling room form a supply air plenum directing the refrigerated air across the produce. A fan is used to create a pressure differential with low pressure in the return air plenum. The pressure differential causes refrigerated air to be pulled through the produce into the return plenum. The return air plenum removes the warmed air from the cooling room and passes the warmed air through to the refrigeration unit. The now-refrigerated air is recycled back into the cooling room, thus completing the air circulation cycle.
A disadvantage with the prior art designs is that air velocity and pressure differential is not uniform throughout the return and supply plenums. The air velocity within the two plenums is highest near the fan. Additionally, the pressure differential between the plenums is also highest near the fan. The lack of uniform air velocity and pressure differential causes the produce to cool unevenly with produce nearest the fan cooling more rapidly than produce farthest from the fan.
An additional disadvantage is that the lack of air velocity and pressure differential uniformity limits the number of pallets of produce that can be cooled in one room.
Another disadvantage is that if a cooling system is to be utilized for a number of fruits and vegetables, the system design must be able to adjust air velocities and adjust pressure differentials between the plenums. Different types of fruits and vegetables require various air velocities for optimum cooling rates. Carton or box design, amount and type of box ventilation, and type of packing liners all impact the pressure differential necessary to move air through the produce.
A further disadvantage is that many produce cooling needs are seasonal. Conventional fixed base forced air cooling rooms service such seasonal markets are idle during the off season.
A number of inventions disclose methods designed to improve uniform air velocity and pressure differential within a forced air cooling room or to provide transportable cooling rooms.
U.S. Pat. No. 5,566,608 Vejdani teaches that placement of the supply and return fans at the end of the cooling room creates a definite length limit to the room such that a single air handling unit can only accommodate a predetermined number of pallets of produce. Vejdani discloses an apparatus placing the air handler on top of the product.
U.S. Pat. No. 4,377,935 Curtis discloses an apparatus that utilizes a sub-floor return air plenum. However, this disclosure is cumbersome to create and does not provide uniform air flow across the pallets of produce.
U.S. Pat. No. 5,789,007 Bianco discloses an apparatus that utilizes multiple top mounted air handlers to provide axial air circulation but does not provide even longitudinal air circulation between the axial partitions.
While the prior art illustrates efforts to cool produce through forced air cooling processes, the prior art does not adequately address the need for uniform management of air velocity and pressure differential along the longitudinal axis of forced air produce cooling supply or return air plenums. Thus, there is a need to provide a forced air produce cooling room that addresses the disadvantages of the prior art.